The Bluetooth system is specified in “Specification of the Bluetooth® System, Covered Core Package Version: 5.0, Publication Date: Dec. 6, 2016 (“Specification of the Bluetooth® System”). Bluetooth operates in the unlicensed Industrial, Scientific, and Medical (ISM) band from 2.400 to 2.4835 GHz. Classic Bluetooth Basic Rate (BR) and Bluetooth Low Energy (BLE) employ Gaussian Frequency-Shift Keying (GFSK) as the primary modulation scheme, while Classic Bluetooth Enhanced Data Rate (EDR) incorporates differential phase-shift keying (DPSK) for increased throughput. BR may occupy any of 79 radio frequency (RF) channels, spaced by 1 MHz, whereas BLE is limited to 40 RF channels, spaced by 2 MHz. For both BR and BLE, the nominal channel symbol rate is 1 MHz, with a nominal channel symbol duration of 1 μs.
A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by first describing relevant Bluetooth system details. Relevant details of the Bluetooth system are therefore presented herein. A more complete description can be obtained by reference to the Specification of the Bluetooth® System, the entirety of which is incorporated herein by reference.
Bluetooth is a time division multiplex (TDM) system that includes a “Master” device, which initiates an exchange of data, and a “Slave” device which responds to the Master. The TDM slot duration is 625 μs, and the maximum payload length is such that certain packet types may extend up to five slots in length. Each device will hop to an RF channel once per packet and Slave devices will utilize the timing of their Master to hop in synchronization.
There are two basic types of data packets and links: Asynchronous Connectionless (ACL) and Synchronous Connection Oriented (SCO). ACL is used for data communications with just one ACL link per device pair. SCO is used for real time audio links, and each device may support up to 3 SCO links at one time.
FIG. 1 is a diagram of the receive/transmit (RX/TX) cycle for the master transceiver in normal mode for single-slot packets. Each TX slot and RX slot is of duration 625 μs. The master transceiver transmits in TX slot 110 on hop channel f(k) and is followed by the RX slot 120, on hop channel f(k+1). The master then transmits in the next slot 130 on hop channel f(k+2). The time between consecutive TX slots and RX slots is therefore 1250 μs. FIG. 2 is a diagram of the corresponding RX/TX cycle of the slave transceiver. The slave transceiver receives during slot 210, on hop channel f(k) and transmits on hop channel f(k+1). The duration of the transmitted packet 140 is less than or equal to 426 μs.
FIG. 3 is a diagram that shows the format of the unique Bluetooth Device Address (BD_ADDR) 300. The BD_ADDR 300 is split into three parts, lower address part (LAP) 310, upper address part (UAP) 320, and non-significant address part (NAP) 330. In order to establish a connection to a Bluetooth device only the UAP and LAP are required. The NAP is informative and devices often use a default NAP to establish connectivity.
The location of wireless devices can be performed by various methods. These methods may be classified as active, passive and combined active and passive. In an active location scheme, a device that is determining the location or range, the measuring device, transmits certain packets to the device being located, the target device, and the common method is to measure the time of arrival (TOA) of the response from the target device and compare that to the time of departure (TOD) that the packet was transmitted by the measuring device so as to determine the time for the round trip (RTT). TOD may be measured for a packet that is transmitted from the measuring station addressed to the target station. The TOA of the response from the target station, at the measuring station, is then also measured. If the turnaround time for the target station to receive the packet from the measuring station and to start to transmit the response is known, then the time difference at the measuring station between the TOA and the TOD, minus the turnaround time at the target station will be directly proportional to twice the distance of the target station from the measuring station. For example, if the target station is a wireless device based upon Bluetooth technology, and if the packet transmitted from the measuring station to the target station is a Poll packet, the response from the target station will generally be a Null packet. The effective turnaround time at the target will be the nominal 625 μs slot time. Hence, the time delay, td, between the measuring station and the target station may be determined from the calculation td=(TOA−TOD−Slot Time)/2 and the distance between the measuring station and the target station is then td×c, where c is the speed of light. This method of estimating the distance to a target station by measuring the TOD and TOA and accounting for the turnaround time is known in the art.
In order to geo-locate a Bluetooth device by measuring the time delay td, a series of packet exchanges may be utilized. In the general sense this requires a regular establishment across several connection layers with security, pairing, and encryption. However, to geo-locate the Bluetooth device such that no interaction from the user of the target device is required, a regular establishment cannot be used.